FIGS. 1 and 2 are partial plan views of lead frames used as a component of a semiconductor device of a dual-in-line package (DIP) type or a small-out line J-Leaded package (SOJ) type. In FIGS. 1 and 2, inner leads are omitted.
Referring to FIG. 1, island supports extend inside of a pair of opposing frame portions 1, 1 and support an island 4. A semiconductor chip 5 is mounted on the island 4. In this condition, the chip 5 and inner leads are bonded together. Thereafter, all of the chip 5, island 4, inner leads, and inner portions of the island support 3, 3 are molded together using mold compound or resin 7.
FIG. 2 shows a different type of tie bars. In each tie bar 3, two support pieces 3A, 3A extend from a frame 1 and join together to form one support piece 3B which is integrally coupled to an island 4.
As seen from FIG. 3, molding is performed in the following manner. The chip 5, island 4 and the like subjected to bonding are held in position using a mold. This mold has a resin injection port 9 (gate) and a cavity 10 communicating with the port 9. Molding resin in a melted state is injected within the cavity. FIG. 4 shows the state where the resin 7 has been injected partially within the cavity 10. Thereafter, the resin 7 is injected into the whole area within the cavity 10 to complete resin molding.
As the resin 7 is injected from the gate 9 as shown in FIG. 3, the resin 7 hits the end surfaces of the island 4 and chip 5 so that they are sometimes twisted about the island supports 3. As the chip 5 and the island 4 become large in size, the amount of resin to be injected becomes large and the injection speed becomes high. Therefore, as the chip 5 and the like become large in size, the above problem of twist or torsion becomes significant. FIG. 4 is a schematic diagram corresponding to the view taken along line VII--VII of FIG. 3, wherein there is shown an example of a semiconductor device whose chip 5 and island 6 are twisted by an angle .theta. about the island supports 3, 3. As seen from FIG. 4, if the chip 5 and the island 4 are twisted, the stress distribution within the cured resin 7 becomes uneven. In a worst case, a crack 11 is formed. Reference numeral 12 in FIG. 4 represents leads.